As shown in FIG. 1 a prior art micro-adjusting device is fastened with a bicycle brake holder A9 by means of a threaded rod A1 and a fastening bolt A11 which is engaged with a threaded hole A91 of the brake holder A9 and the threaded rod A1. The prior art device is in fact mounted on the threaded rod A1 in conjunction with the fastening bolt A11 and is composed of a cap A2, a spring A3, a spring member A4, a fastening shaft A5, a spring actuating piece A6, a washer A10. The spring, A3 has one end A31 located in a recess A61 of the spring actuating piece A6, and another end A32 fastened with the bicycle frame via a round hole A21 of the cap A2. As an adjusting rod A8 is rotated, a retaining projection A62 of the spring actuating piece A6 is urged such that the spring A3 is displaced to attain the microadjustment of the brake holder.
Such a prior art micro-adjusting device as described above is defective in design in that the spring actuating piece A6 is entirely concealed in the spring housing member A4 such that the contact between the retaining projection A62 of the spring actuating piece A6 and the adjusting rods A8 cannot be observed with the naked eye, and that the adjusting rod A8 cannot be easily rotated at such time when one end A31 of the sprig A3 is urged intensively by the spring actuating piece A6.